8 research outputs found
Nitrogen Management at the Whole Plant Level for Better Nitrogen Use Efficiency
No full textInternational audienceNitrogen fertilizers are used worldwide and are essential to obtain good yields in cereals, oilseed rape and maize. However, nitrogen fertilizers have a negative impact on the carbon balance and in some case on environment. Decreasing fertilizer needs without affecting yield would be beneficial to farmers’ costs and to environment. Then understanding how plants uptake fertilizers, their preference amongst the different nitrogen sources, how they assimilate inorganic nitrogen forms and how they recycle and reuse nitrogen all along their lifespan is essential for better use efficiency (NUE). This keynote lecture will focus on nitrogen assimilation, recycling and remobilization in plant and will show how our recent knowledge led us to propose breeding solutions to improve NUE and plant adaptation to environment.Chen, Q., Soulay, F., Saudemont, B., Elmayan, T., Marmagne, A., and Masclaux-Daubresse, C.(2019): Overexpression of ATG8 in Arabidopsis Stimulates Autophagic Activity and Increases NitrogenRemobilization Efficiency and Grain Filling, Plant and Cell Physiology (60), 343-352.Guiboileau, A., Yoshimoto, K., Soulay, F., Bataille, M.P., Avice, J.C., and Masclaux-Daubresse, C.(2012): Autophagy machinery controls nitrogen remobilization at the whole-plant level under bothlimiting and ample nitrate conditions in Arabidopsis, New Phytologist (194), 732-740.James, M., Masclaux-Daubresse, C., Marmagne, A., Azzopardi, M., Laine, P., Goux, D., Etienne, P.,and Trouverie, J. (2019): A New Role for SAG12 Cysteine Protease in Roots of Arabidopsis thaliana.Frontiers in Plant Science (9).James, M., Poret, M., Masclaux-Daubresse, C., Marmagne, A., Coquet, L., Jouenne, T., Chan, P.,Trouverie, J., and Etienne, P. (2018): SAG12, a Major Cysteine Protease Involved in NitrogenAllocation during Senescence for Seed Production in Arabidopsis thaliana, Plant and Cell Physiology(59), 2052-2063.Masclaux-Daubresse, C., Chen, Q., and Havé, M. (2017): Regulation of nutrient recycling viaautophagy, Current Opinion in Plant Biology (39), 8-17.Moison, M., Marmagne, A., Dinant, S., Soulay, F., Azzopardi, M., Lothier, J., Citerne, S., Morin, H.,Legay, N., Chardon, F., Avice, J.C., Reisdorf-Cren, M., and Masclaux-Daubresse, C. (2018): Threecytosolic glutamine synthetase isoforms localized in different-order veins act together for Nremobilization and seed filling in Arabidopsis, Journal of Experimental Botany (69), 4379-4393.Tegeder, M., and Masclaux-Daubresse, C. (2018): Source and sink mechanisms of nitrogen transportand use, New Phytologist (217), 35-53
Identification of Barley (Hordeum vulgare L.) Autophagy Genes and Their Expression Levels during Leaf Senescence, Chronic Nitrogen Limitation and in Response to Dark Exposure
No full textBarley is a cereal of primary importance for forage and human nutrition, and is a useful model for wheat. Autophagy genes first described in yeast have been subsequently isolated in mammals and Arabidopsis thaliana. In Arabidopsis and maize it was recently shown that autophagy machinery participates in nitrogen remobilization for grain filling. In rice, autophagy is also important for nitrogen recycling at the vegetative stage. In this study, HvATGs, HvNBR1 and HvATI1 sequences were identified from bacterial artificial chromosome (BAC), complementary DNA (cDNA) and expressed sequence tag (EST) libraries. The gene models were subsequently determined from alignments between genome and transcript sequences. Essential amino acids were identified from the protein sequences in order to estimate their functionality. A total of twenty-four barley HvATG genes, one HvNBR1 gene and one HvATI1 gene were identified. Except for HvATG5, all the genomic sequences found completely matched their cDNA sequences. The HvATG5 gene sequence presents a gap that cannot be sequenced due to its high GC content. The HvATG5 coding DNA sequence (CDS), when over-expressed in the Arabidopsis atg5 mutant, complemented the plant phenotype. The HvATG transcript levels were increased globally by leaf senescence, nitrogen starvation and dark-treatment. The induction of HvATG5 during senescence was mainly observed in the flag leaves, while it remained surprisingly stable in the seedling leaves, irrespective of the leaf age during stress treatment
Une orbitopathie inflammatoire révélant un lymphome primitif non hodgkinien du sinus maxillaire : à propos d’un cas
No full textLes lymphomes malins non hodgkiniens (LMNH) sont des tumeurs rares du sinus maxillaire. Leurs manifestationscliniques sont souvent discrètes et peu spécifiques, ce qui explique les difficultés diagnostiques.Le diagnostic positif repose sur l’imagerie par tomodensitométrie et sur la confirmation histologique. Ilfaut souligner que la prise de corticoïdes peut modifier la présentation clinique et histopathologique deces tumeurs, ce qui cause un retard diagnostique et donc un retard de prise en charge thérapeutique
Interaction between leaf senescence and resource allocation for seed filling in Arabidopsis thaliana
No full textInternational audienc
Physiological and metabolic consequences of autophagy deficiency for the management of nitrogen and protein resources in Arabidopsis leaves depending on nitrate availability
No full textAutophagy is present at a basal level in all plant tissues and is induced during leaf ageing and in response to nitrogen (N) starvation. Nitrogen remobilization from the rosette to the seeds is impaired in autophagy mutants. This report focuses on the role of autophagy in leaf N management and proteolysis during plant ageing.
Metabolites, enzyme activities and protein contents were monitored in several autophagy-defective (atg) Arabidopsis mutants grown under low and high nitrate conditions.
Results showed that carbon (C) and N statuses were affected in atg mutants before any senescence symptoms appeared. atg mutants accumulated larger amounts of ammonium, amino acids and proteins than wild type, and were depleted in sugars. Over-accumulation of proteins in atg mutants was selective and occurred despite higher endopeptidase and carboxypeptidase activities. Specific over-accumulation of the ribosomal proteins S6 and L13 subunits, and of catalase and glutamate dehydrogenase proteins was observed. atg mutants also accumulated peptides putatively identified as degradation products of the Rubisco large subunit and glutamine synthetase 2 (GS2). Incomplete chloroplast protein degradation resulting from autophagy defects could explain the higher N concentrations measured in atg rosettes and defects in N remobilization.
It is concluded that autophagy controls C : N status and protein content in leaves of Arabidopsis
Autophagy machinery controls nitrogen remobilization at the whole‐plant level under both limiting and ample nitrate conditions in Arabidopsis
No full textProcesses allowing the recycling of organic nitrogen and export to young leaves and seeds are important determinants of plant yield, especially when plants are nitrate-limited. Because autophagy is induced during leaf ageing and in response to nitrogen starvation, its role in nitrogen remobilization was suspected. It was recently shown that autophagy participates in the trafficking of Rubisco-containing bodies to the vacuole. To investigate the role of autophagy in nitrogen remobilization, several autophagy-defective (atg) Arabidopsis mutants were grown under low and high nitrate supplies and labeled with at the vegetative stage in order to determine 15N partitioning in seeds at harvest. Because atg mutants displayed earlier and more rapid leaf senescence than wild type, we investigated whether their defects in nitrogen remobilization were related to premature leaf cell death by studying the stay-green atg5.sid2 and atg5.NahG mutants. Results showed that nitrogen remobilization efficiency was significantly lower in all the atg mutants irrespective of biomass defects, harvest index reduction, leaf senescence phenotypes and nitrogen conditions. We conclude that autophagy core machinery is needed for nitrogen remobilization and seed filling
The contrasting N management of two oilseed rape genotypes reveals the mechanisms of proteolysis associated with leaf N remobilization and the respective contributions of leaves and stems to N storage and remobilization during seed filling.
No full textBACKGROUND: Oilseed rape is the third largest oleaginous crop in the world but requires high levels of N fertilizer of which only 50% is recovered in seeds. This weak N use efficiency is associated with a low foliar N remobilization, leading to a significant return of N to the soil and a risk of pollution. Contrary to what is observed during senescence in the vegetative stages, N remobilization from stems and leaves is considered efficient during monocarpic senescence. However, the contribution of stems towards N management and the cellular mechanisms involved in foliar remobilization remain largely unknown. To reach this goal, the N fluxes at the whole plant level from bolting to mature seeds and the processes involved in leaf N remobilization and proteolysis were investigated in two contrasting genotypes (Aviso and Oase) cultivated under ample or restricted nitrate supply.
RESULTS: During seed filling in both N conditions, Oase efficiently allocated the N from uptake to seeds while Aviso favoured a better N remobilization from stems and leaves towards seeds. Nitrate restriction decreased seed yield and oil quality for both genotypes but Aviso had the best seed N filling. Under N limitation, Aviso had a better N remobilization from leaves to stems before the onset of seed filling. Afterwards, the higher N remobilization from stems and leaves of Aviso led to a higher final N amount in seeds. This high leaf N remobilization is associated with a better degradation/export of insoluble proteins, oligopeptides, nitrate and/or ammonia. By using an original method based on the determination of Rubisco degradation in the presence of inhibitors of proteases, efficient proteolysis associated with cysteine proteases and proteasome activities was identified as the mechanism of N remobilization.
CONCLUSION: The results confirm the importance of foliar N remobilization after bolting to satisfy seed filling and highlight that an efficient proteolysis is mainly associated with (i) cysteine proteases and proteasome activities and (ii) a fine coordination between proteolysis and export mechanisms. In addition, the stem may act as transient storage organs in the case of an asynchronism between leaf N remobilization and N demand for seed filling
Arabidopsis thaliana ASN2 encoding asparagine synthetase is involved in the control of nitrogen assimilation and export during vegetative growth
No full textWe investigated the function of ASN2, one of the three genes encoding asparagine synthetase (EC 6.3.5.4), which is the most highly expressed in vegetative leaves of Arabidopsis thaliana. Expression of ASN2 and parallel higher asparagine content in darkness suggest that leaf metabolism involves ASN2 for asparagine synthesis. In asn2-1 knockout and asn2-2 knockdown lines, ASN2 disruption caused a defective growth phenotype and ammonium accumulation. The asn2 mutant leaves displayed a depleted asparagine and an accumulation of alanine, GABA, pyruvate and fumarate, indicating an alanine formation from pyruvate through the GABA shunt to consume excess ammonium in the absence of asparagine synthesis. By contrast, asparagine did not contribute to photorespiratory nitrogen recycle as photosynthetic net CO2 assimilation was not significantly different between lines under both 21 and 2% O2. ASN2 was found in phloem companion cells by in situ hybridization and immunolocalization. Moreover, lack of asparagine in asn2 phloem sap and lowered 15N flux to sinks, accompanied by the delayed yellowing (senescence) of asn2 leaves, in the absence of asparagine support a specific role of asparagine in phloem loading and nitrogen reallocation. We conclude that ASN2 is essential for nitrogen assimilation, distribution and remobilization (via the phloem) within the plant
